#include <bits/stdc++.h>
using namespace std;
typedef unsigned long long ul;
typedef signed long long ll;
ul over = 1000000007;

int main(void)
{
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed;
  for (int i = 0; i < 9; ++i) {
    int b;
    cin >> b;
    if (b != i+1) {cout << i+1 << endl; return 0;}
  }
  cout << 10 << endl;
  return 0;
}